US President Joe Biden was notably hoarse Friday as he delivered a speech and answered questions from the press, but insisted he had simply caught a cold from his grandson, and his doctor said his Covid tests were negative.

The gravelly, lower-pitched tone of Biden's voice as he spoke at the White House, peppered with several coughs, prompted the first journalist called on to ask, "Are you okay?"

"I am okay," Biden said. "I have a test every day... a Covid test. They check me for all the strains.

"What I have is a 1 1/2-year-old grandson who had a cold who likes to kiss his pop... but it's just a cold," he added.

The arrival of winter hand-in-hand with the emergence of the new Omicron coronavirus variant have raised fears of a potential resurgence of Covid-19 cases, particularly as Americans gather for end-of-year festivities.

Biden, 79, spent last week's Thanksgiving holiday with his family.

He is the oldest president ever elected in the United States, making his health of particular concern.

Earlier in November, he underwent an extensive but routine checkup, after which White House physician Kevin O'Connor said the president was "healthy" and "vigorous."

After Biden's public appearance on Friday, O'Connor confirmed that Biden "is experiencing some increased nasal congestion this week."

"This can be heard in his voice and he is feeling the colloquially well-known 'frog in ones throat'," the doctor said in a statement released by the White House.

O'Connor said the president had been tested for 19 common respiratory diseases, including three tests this week for Covid-19, and that all the tests were negative.